Opposition MPs believe more resources should be dedicated to investigating and preventing fraud in the rebuild.

The Press has previously reported that SFO investigators searched the head office of Maincom NZ in Woolston in February. The small to medium-sized company carries out repairs for EQC under the home repair scheme.

One of the company's directors, Warren Bale, confirmed he was being personally investigated. He denied any wrongdoing. The company had co-operated fully with authorities, Bale said.

Yesterday, the SFO confirmed its probe into the company was ongoing. It refused to provide details of the other active rebuild-related investigations.

"The release of such information could have a chilling effect on the ongoing voluntary provision of information," SFO general counsel Mark Williams said.

NZ First leader Winston Peters yesterday continued to claim he had information about dubious dealings in the rebuild which warranted investigation by the SFO "a long, long time ago".

Peters would not name names, but said some of the allegations related to companies that had invoiced for work that had not been completed. Authorities had been alerted, he said.

Police Minister Anne Tolley said any information the SFO received that warranted scrutiny would be investigated.

"To claim the SFO would not do this is complete nonsense and blatant electioneering," she said.

The SFO's funding was cut by $1.8 million in this year's Budget after a three-year boost to cope with investigations stemming from the collapse of various finance companies.

Peters said the Government had ignored warnings from international experts about white collar crime post-quake and failed to devote resources to the issue.

Labour MP Jacinda Ardern said the SFO's budget did not allow for a preventative approach to rebuild-related fraud.

Tolley said the SFO worked with organisations like the Canterbury Earthquake Recovery Authority, police and insurance companies to identify risks and prevent fraud.

In March, The Press reported a major SFO investigation into post-quake fraud in Christchurch relied on an informant whose business dealings are now the subject of a police complaint.

The SFO probe between July, 2012, and April last year failed to uncover "evidence of serious and complex fraud". It was sparked by a complaint from Lumley Insurance, which suspected contractors were inflating their earthquake damage assessments/costings.

An investigation by The Press showed the SFO's main informant was builder Craig Johnson, 29, whose company, NZ Premium Construction, went into liquidation in February with debts of nearly $2 million.